A turbomachine comprises a high pressure compressor having its downstream end opening out to the inlet of a combustion chamber. In certain configurations, where it is desirable to reduce the axial size of the turbomachine, the last compression stage is a centrifugal stage having its outlet surrounded by a radial annular diffuser that is connected to an annular nozzle opening out to the inlet of the combustion chamber. The nozzle comprises a radially inner wall forming a surface of revolution that carries a plurality of vanes surrounded on the outside by a casing that extends downstream around the combustion chamber.
When cold, clearance is provided between the radially outer ends of the vanes of the nozzle and the outer casing. In operation, the nozzle expands radially to a greater extent than the casing, and the radially outer ends of the vanes come into contact with the outer casing. The clearance at the tops of the vanes of the nozzle is defined in such a manner as to guarantee that the radially outer ends of the vanes of the nozzle press against the casing with a force that is small enough to avoid excessively stressing the casing in operation since it is already subjected to large pressure variations due to fuel combustion in the chamber downstream from the high pressure compressor.
Nevertheless, the cold clearance at the tops of the vanes can be defined for only one particular stage of flight, for example a cruising stage since that is the stage that lasts the longest. During other stages of flight, the radially outer ends of the vanes of the nozzle either do not make contact with the casing, thereby allowing air to flow between the tops of the vanes and the casing and thus disturbing the flow of air towards the combustion chamber, or else the tops of the vanes exert excess pressure against the casing. Furthermore, when the ends of the vanes are not pressed against the casing, the nozzle is subjected to vibration.